1. Field of the Invention
The present invention relates to a magnetic recording and reproducing apparatus including a magnetic recording medium such as a discrete track medium or patterned medium and a control method thereof, a magnetic recording medium, and a stamper for manufacturing of a magnetic recording medium.
2. Description of the Related Art
A magnetic recording and reproducing apparatus including a magnetic recording medium on which positioning information used for positioning control for a magnetic head is recorded has been conventionally known.
FIG. 17 shows an exemplary magnetic recording medium included in the conventionally known magnetic recording and reproducing apparatus.
The magnetic recording medium 100 shown in FIG. 17 has a plurality of servo region 102 radially formed at predetermined intervals. A concavo-convex pattern formed by a magnetic layer forms each servo region 102.
Servo information is stored in the servo region 102. As shown in FIG. 18 that shows the servo region 102 in an enlarged state, the servo information includes a preamble portion 104, a servo mark portion 106, an address portion 108 in which address information is stored, and a burst portion 110 in which position information is stored. User data is to be recorded on data tracks 112 as shown in the same figure.
A burst pattern formed by four types of burst signal groups 110A, 110B, 110C, and 110D is formed as the position information in the burst portion 110 of the servo region 102. The burst signal groups 110A and 110B are arranged as a pair of position information in such a manner that they each symmetrically extend with respect to the center line of the corresponding data track 112. The burst signal groups 110C and 110D are arranged as another pair of position information at positions shifted from the burst signal groups 110A and 110B by a half of a track pitch, respectively.
FIG. 19 is an enlarged view of the burst signal group 110A. The other burst signal groups 110B, 110C, and 110D also have the same structure as that of the burst signal group 110A.
As shown in FIG. 19, the burst signal group 110A (110B, 110C, or 110D) is formed by a plurality of (about 10 to 30 in a typical case) concavo-convex patterns arranged in a circumferential direction. In the concavo-convex pattern, convex portions (mesh portions in FIG. 19) formed by a magnetic layer (magnetic material) have a length BL1 in the circumferential direction and a radial width BW1 in a radial direction, and concave portion have a length BL2 in the circumferential direction. In general, the magnetic recording and reproducing apparatus rotates the magnetic recording medium 100 at a constant angular velocity. Thus, the circumferential length BL1 of the convex portion and the circumferential length BL2 of the concave portion are varied depending on their positions in the radial direction on the magnetic recording medium 100, and they become longer from an inner circumferential side to an outer circumferential side of the magnetic recording medium 100.
The burst pattern in the burst portion 110 is formed by arranging each burst signal group (110A, 110B, 110C, or 110D) at a plurality of positions at an interval BW2 in the radial direction, as shown in FIG. 20.
A position control circuit 124 reproduces the above burst pattern. An exemplary position control circuit 124 is shown in FIG. 21. This position control circuit 124 is composed of an amplifier 116 that amplifies reproduced signal read by a magnetic head 114, a signal processing circuit 118 (that comprises an LPF (Low Pass Filter) 118A, an HPF (High Pass Filter) 118B, and an amplitude detector 118C), a sample hold unit 120 that holds position control signal after signal processing, and a differential amplification circuit 122.
After the burst pattern recorded on the magnetic recording medium 100 is read by the magnetic head 114, the reproduced signal of the burst pattern is amplified by the amplifier 116 and is then input to the signal processing circuit 118. The reproduced signal input into the signal processing circuit 118 is output to the sample hold unit 120 as position control signal after only the fundamental wave component of the reproduced signal is extracted. The sample hold unit 120 holds the position control signals of the burst signal groups 110A, 110B, 110C, and 110D. The differential amplifier 122 obtains an output difference between the position control signals of the burst signal groups 110A and 110B or between the position control signals of the burst signal groups 110C and 110D, thereby acquiring position information of the magnetic head 114. In this manner, positioning (tracking) control for the magnetic head 114 is carried out (refer to Japanese Patent Laid-Open Publication No. Hei 7-78432 for example).
However, in case of a magnetic recording medium such as a discrete track medium and a patterned medium, on which the burst pattern (position information) is recorded by the concavo-convex pattern formed by the magnetic layer, a magnetization signal of the concavo-convex pattern is recorded with unidirectional polarity. Thus, the reproduced signal of the concavo-convex pattern has a waveform shown in FIG. 22. In FIG. 22, mesh portions represent a plan view of the convex portions in the concavo-convex pattern. Please note that the reproduced signal waveform of the concavo-convex pattern in FIG. 22 is an example in the case where the magnetic layer is a perpendicular magnetic recording layer.
In that magnetic recording medium in which the burst pattern is recorded by the concavo-convex pattern formed by the magnetic layer, the output level of the position control signal used for positioning control for the magnetic head is about half, as compared with a conventional continuous-layer medium in which a magnetization signal of a concavo-convex pattern is recorded with bidirectional polarity. Thus, improvement of the position control for the magnetic head has a limitation.